Aflatoxin biosynthetic pathway extrolites in airborne Aspergilli series Versicolores

The Aspergilli of the series Versicolores include several airborne species to which we are exposed daily. Most of them synthesise sterigmatocystin, a mycotoxin precursor of aflatoxins recognised as potentially carcinogenic for humans (group 2B) by the International Agency for Research on Cancer. Our objective was to study the potential role of these moulds in the synthesis of extrolites of the aflatoxin biosynthetic pathway. A total of 124 isolates belonging to the eight species of the series Versicolores collected in French bioaerosols were studied: Aspergillus amoenus (n=1), Aspergillus creber (n=45), Aspergillus fructus (n=2), Aspergillus jensenii (n=39), Aspergillus protuberus (n=6), Aspergillus puulaauensis (n=5), Aspergillus sydowii (n=14) and Aspergillus tabacinus (n=2). All these isolates and a reference strain of each species were extracted using ethyl acetate acidified with 1% (v/v) acetic acid. In each extract, we screened for the following extrolites of the aflatoxin biosynthetic pathway by UPLC-HRMS: norsolorinic acid, versicolorin A, 6-demethylsterigmatocystin, sterigmatocystin, 8-O-methylsterigmatocystin, 5-methoxysterigmatocystin and aflatoxins B-1, B-2, G(1) and G(2). All extrolites, except aflatoxins, were found variably among species. Sterigmatocystin was found in extracts of all eight Versicolores species, including A. sydowii and A. tabacinus whose ability to synthesise sterigmatocystin was questioned or unknown, respectively.